Method and apparatus for refrigeration

ABSTRACT

Apparatus is disclosed for refrigerating a moist article, the apparatus comprising a cold room, means for circulating cooling atmosphere through the cold room, a moisture absorbent liquid cooling spray in the path of said atmosphere, means for collecting and recirculating the liquid in a continuous path, means for admitting a cryogenic cooling fluid to the liquid and means for removing the fluid and absorbed moisture from the liquid before the liquid returns to the spray.

This invention relates to reducing the temperature of articlesparticularly foodstuffs for short or long term storage.

The introduction of cryogenic fluids such as liquid nitrogen intomechanical air blast freezer rooms improves their performancedramatically. There are believed to be two main inter-related benefits.The first is a very rapid removal of heat during the first hour offreezing, which is beyond the normally designed capabilities ofmechanical freezing, and brings the temperature of the skin of theproduct rapidly to freezing point and hence seals in moisture.

The second benefit is associated with the dry atmosphere caused by theinjection of liquid nitrogen. Moisture coming out of the product beingfrozen is rapidly purged out of the room by the large volume of nitrogengas generated which is continually exhausted from the room. Thus themoisture lost from the product cannot freeze-out and collect on thecoils of the mechanical refrigerating units through which a liquidrefrigerant circulates to cool the air blast. Normally this freezing-outis significant and blinds the coils thereby reducing the efficiency ofthe units and slows down the freezing of the product because of theextra temperature differential across the ice which severely limits thecapacity of the refrigeration equipment by reducing evaporatortemperatures.

One means of achieving an improvement in air blast freezer rooms is bythe introduction into the room of a cryogenic fluid such as liquidnitrogen. However, a very significant disadvantage of such liquidnitrogen boosting is that the freezer room atmosphere is unfavourable tohuman life. Since the product is usually loaded by hand on overheadrails, or by fork lift, the room must be equipped with fairly elaboratesafety controls to prevent suffocation of loading and unloading staff.

It is an object of the present invention to provide means forrefrigerating a moist article whereby a non-toxic cooling atmosphere canbe employed and where means are provided for removing moisture from theatmosphere.

According to the invention there is provided apparatus for refrigeratinga moist article comprising a cold room, means for circulating coolingatmosphere through said cold room, a moisture absorbent liquid coolingspray in the path of said atmosphere, means for collecting andrecirculating said liquid in a continuous path, means for admitting acryogenic cooling fluid to said liquid and means for removing said fluidand absorbed moisture from said liquid before said liquid returns tosaid spray.

The invention also provides a method of refrigerating a moist articlecomprising the steps of circulating a cooling atmosphere past saidarticle, cooling said atmosphere by contact with a moisture absorbentliquid spray, collecting and recirculating said liquid, cooling saidliquid by bringing it into contact with a cryogenic fluid and removingsaid fluid and any absorbed moisture from said liquid before returningsaid liquid to said article.

Preferred embodiments of the invention will now be described, by way ofexample only, with reference to the accompanying drawings in which:

FIG. 1 is a sectional side elevation of refrigeration apparatusaccording to the invention;

FIG. 2 is a view taken on line 2--2 of FIG. 1;

FIG. 3 is a sectional side elevation showing a modification to theembodiment of FIG. 1.

Referring initially to FIGS. 1 and 2 of the drawings, a cold room showngenerally by numeral 10 is enclosed by heat insulating walls 11 andsealed by an access door 12. Located within the room is a frame 13supporting rails 14 from which are suspended the articles to be frozen15. The frame 13 also supports a pair of contact air coolers 16 withinthe cold room 10.

Each cooler 16 is provided with a plurality of downwardly directed spraynozzles 17 for spraying a cooling liquid into a trough 18 locateddirectly beneath them. A fan 19 associated with each cooler circulatescooling air through the open ended cooler and then down through the coldroom, past the articles to be frozen and back to the cooler.

The cooling liquid is preferably a brine solution including calciumchloride and propylene glycol but it will be appreciated that anysuitable liquid may be used. Liquid collected in the trough passes downthrough conduit 20 through a non-return valve 21 to a gas-lift pipe 22having an inlet port 23 through which a cryogenic fluid is admitted. Thecryogenic fluid is preferably liquid nitrogen but again, any suitablefluid may be used.

Upon admission to the pipe 23 the fluid cools the circulating liquid andboils, rising in the pipe and carrying the liquid with it through athrottle valve 24 and into a separator tank 25. The cryogenic gas thenescapes to atmosphere through vent 26 while the liquid passes into abrine concentrator 27 prior to returning to the spray nozzles 17 throughgallery pipe 28. The concentrator monitors and adjusts the specificgravity of the brine by known means, admitting additional brineconcentrate as required through port 29.

Moisture evaporating from the articles within the cold rooms is absorbedas a liquid by the brine spray as the cooling atmosphere traverses thecooler. Once in contact with the cryogenic fluid, however, the moisturefreezes out as ice particles which are strained out of the brine by aremovable filter 30 located within the separator tank 25. Some of themoisture may be carried out through vent 26 with the cryogenic gas.

Known temperature and liquid level sensors are preferably located withinthe separator tank to control the admission of cryogenic fluid throughinlet port 23 and the rate of flow through throttle valve 24respectively. An intermediate pipe 31 is preferably provided to act as asyphon breaker.

Preferably, the cold room also includes a conventional forced draughtcooler unit 32, located between the spray coolers 16.

In another embodiment as shown in FIG. 3, the gas-lift system isreplaced with a pump. In this arrangement, brine from the coolers 16 isdirected by gravity feed through pipe 20 to a holding tank 33. A gassparging head 34 is located in the lower portion of the tank to receiveliquid nitrogen from pipe 35. A pump 36 receives brine cooled by theliquid nitrogen and pumps it to the separator tank 25 through pipe 37.The speed of the pump is preferably controlled in known manner by aliquid level sensor in the separator tank.

Although the invention has been described with reference to specificexamples, it will be appreciated by those skilled in the art that theinvention may be embodied in many other forms.

I claim:
 1. Apparatus for refrigerating a moist article comprising acold room, means for circulating cooling atmosphere through said coldroom, means for spraying a moisture absorbent liquid cooling spray inthe path of said atmosphere, collecting means in said room forcollecting said liquid and means connected to said collection means forrecirculating said liquid in a continuous path back to said sprayingmeans, means connected to said recirculating means for admitting acryogenic cooling fluid to said liquid and means connected to saidrecirculating means for removing said fluid and absorbed moisture fromsaid liquid before said liquid returns to said spray.
 2. Apparatus asclaimed in claim 1 wherein said spray is located within said cold room.3. Apparatus as claimed in claim 1 including a separator tank upstreamof said spray and means for admitting said fluid downstream of saidspray and upstream of said tank, said tank including means for ventingsaid fluid and trapping said moisture.
 4. Apparatus as claimed in claim3 wherein said liquid is circulated by said fluid rising towards saidtank.
 5. Apparatus as claimed in claim 1 wherein said liquid iscirculated by a pump.
 6. Apparatus as claimed in claim 1 wherein saidliquid is a brine solution containing calcium chloride.
 7. Apparatus asclaimed in claim 1 wherein said liquid is a brine solution containingpropylene glycol.
 8. Apparatus as claimed in claim 1 wherein said fluidis liquid nitrogen.
 9. Apparatus as claimed in claim 1 wherein saidfluid is liquid carbon dioxide.